WASHINGTON (Reuters) - Ford Motor Co <F.N> said on Friday it will offer free repairs to North American owners of more than 1.4 million Explorer sport utility vehicles to help ensure that carbon monoxide and other exhaust gases cannot get into the vehicles, following the U.S. government's decision to upgrade an investigation in July.

Several U.S. police agencies have raised concerns about potentially deadly carbon monoxide gas entering the cabins of Ford Explorers that had been adapted for law enforcement uses. Federal regulators have said they are aware of more than 2,700 complaints for exhaust odors as well as reports of three crashes and 41 injuries that may be linked to exposure to carbon monoxide among police and civilian 2011-2017 Explorer vehicles.

Ford said its investigation has not found "carbon monoxide levels that exceed what people are exposed to every day" in the 1.4 million civilian vehicles. There is no U.S. government standard for in-vehicle carbon monoxide levels. Ford says it believes the vehicles are safe and is making the offer, which it is not classifying as a recall, in response to customer concerns.

The second largest U.S. automaker said starting November 1, dealers will reprogram the air conditioner, replace the liftgate drain valves and inspect sealing of the rear of the vehicle. The fix covers about 1.3 million U.S. vehicles and about 100,000 in Canada and Mexico.

Ford declined to comment on the potential financial impact of the service offer that will last through the end of 2018.

Ford shares fell 0.7 percent to $12.04 in afternoon trading.

The U.S. National Highway Traffic Safety Administration (NHTSA) in July upgraded and expanded a probe into 1.33 million Ford Explorer SUVs over reports of exhaust odors in vehicle compartments and exposure to carbon monoxide.

Police agencies have reported two crashes that may be linked to carbon monoxide exposure and a third incident involving injuries related to carbon monoxide exposure.

NHTSA said it is evaluating preliminary testing that suggests carbon monoxide levels may be elevated in certain driving scenarios.

Ford has issued four technical service bulletins related to the exhaust odor issue to address complaints from police fleets and other owners.

In July, Ford said it would pay to repair police versions of its Ford Explorer SUVs to correct possible carbon monoxide leaks that may be linked to crashes and injuries after some police reports temporarily halted use of the vehicles over carbon monoxide concerns.

The city of Austin, Texas said in July it would remove all 400 of the city’s Ford Explorer SUVs from use for additional testing and repairs after the city said 20 police officers were found with elevated levels of carbon monoxide. The department returned the vehicles to service after repairs and testing.

In 2016, Ford agreed to settle a U.S. class-action lawsuit involving 1 million 2011-2015 Explorer SUVs over exhaust odor complaints, including reimbursements of up to $500 for repairs and the company agreed to make repairs. That settlement was approved in June but has not taken effect because of a penidng appeal.